1. Field of the Invention
The present invention relates to a correcting substrate for a charged particle beam lithography apparatus for example, a correcting substrate which corrects a stage position of a lithography apparatus which writes a pattern on a target object by using an electron beam.
2. Related Art
A lithography technique which leads development of micropatterning of a semiconductor device is a very important process which generates a pattern in semiconductor manufacturing processes. In recent years, with an increase in integration density of an LSI, a circuit line width required for a semiconductor device is further miniaturized each year. In order to form a desired circuit pattern on such a semiconductor device, a high-precision original pattern (also called a reticle or a mask) is necessary. In this case, an electron beam pattern writing technique essentially has an excellent resolution, and is used in production of high-precision original patterns.
FIG. 12 is a conceptual diagram for explaining an operation of a conventional variable-shaped electron beam lithography apparatus.
The operation of the variable-shaped electron beam (EB: Electron Beam) lithography apparatus will be described below. In a first aperture plate 410, an oblong, for example, rectangular opening 411 to shape an electron beam 330 is formed. In a second aperture plate 420, a variable-shaped opening 421 to shape the electron beam 330 passing through the opening 411 of the first aperture plate 410 into a desired oblong shape is formed. The electron beam 330 irradiated from the charged particle source 430 and passing through the opening 411 of the first aperture plate 410 is deflected by a deflector, passes through a part of the variable-shaped opening 421 of the second aperture plate 420, and is irradiated on a target object 340 placed on a stage continuously moving in one predetermined direction (for example, direction X). More specifically, an oblong shape which can pass through both the opening 411 of the first aperture plate 410 and the variable-shaped opening 421 of the second aperture plate 420 is written in a pattern writing region on the target object 340 placed on the stage continuously moving in the direction X. The scheme that causes a beam to pass through the opening 411 of the first aperture plate 410 and the variable-shaped opening 421 of the second aperture plate 420 to form an arbitrary shape is called a variable-shaping scheme (for example, see Published Unexamined Japanese Patent Application No. 2007-294562).
In this case, in the electron beam lithography apparatus, the position of a stage on which a target object such as a mask substrate is placed is measured by a length measuring device using, for example, a laser interferometer to determine a beam irradiation position. At this time, a mirror which reflects the laser is arranged on the stage. With passage of time, distortion or the like of the mirror may change, and an error may occur at a global pattern writing position. For this reason, in the electron beam lithography apparatus, a process of correcting a position error caused by mirror distortion or the like is performed by using a correcting substrate on which patterns are regularly arranged. The following substrate is used as a conventional correcting substrate. That is, a metal film is deposited on a glass substrate including silicon oxide (SiO2) and the metal film is completely removed according to a pattern portion for global position error correction. For this reason, a glass surface is exposed on the pattern portion from which the metal film is removed. An electron beam is irradiated on the correcting substrate, and reflected electrons are detected so that a process of measuring a pattern position to correct an error is performed. However, when electron beam scanning is performed by using the correcting substrate, the exposed glass substrate is electrically charged. For this reason, an unexpected measurement error disadvantageously occurs.
As a correcting substrate, a substrate having the pattern portion from which a metal film is not completely removed and on which the metal film is slightly left is used. Electronic charging can be avoided when electron beam scanning is performed by using the correcting substrate formed to slightly leave the metal film thereon. However, since the pattern portion and the other portion include a metal having equal electron reflectances, contrast is determined by only a step of the pattern. For this reason, a position resolution is not preferable, and accurate measurement cannot be easily performed.
Furthermore, in any one of the correcting substrates, the substrate itself thermally expands due to heat generation of the glass substrate by electron beam irradiation to cause an error.
As described above, problems such as electron charging and deterioration of contrast are posed. Furthermore, a position error caused by thermal expansion of the glass substrate is another problem. With micropatterning of recent patterns, a correcting substrate which solves the above problems to perform accurate position correction is required to be developed.